CO laser-probing technique

The formation of CO from O 4- CS has been studied by infrared chemiluminescence (analysis of steady-state populations), by the chemical laser method and by laser probe techniques. Good agreement exists for the relative populations in v = 6-15. The disagreement over the populations of the lower levels recently was resolvedby the discovery that the O 4- CSg reactions, which in most systems accompanies the O 4- CS reaction, yields CO in the lower levels. Following the suggestion of Kelley, the lower levels in Table 2.13 were obtained from extrapolation of the linear... 

A modern variation on the rapid scan spectrometer, which is under development, uses a laser-generated plasma as a high intensity broad-band IR source (65). This method has been used to probe the vc—o absorption of W(CO)6. Another technique TRISP (time-resolved IR spectral photography), which involves up-conversion of IR radiation to the visible, has also been used to probe transients (66). This method has the enormous advantage that efficient phototubes and photodiodes can be used as detectors. However, it is a technically challenging procedure with limitations on the frequency range which depend on the optical material used as an up-converter. 

Schoenung, S. M., and R. K. Hanson. 1981. CO and temperature measurements in a flat flame by laser absorption spectroscopy and probe techniques. Combustion Science Technology 24 227-37. 

CO2 is the gas generally used for mass-spectrometric analysis. More recently CO and O2 have also been used in high temperature conversion of organic material and in laser probe preparation techniques. A wide variety of methods have been described to liberate oxygen from the various oxygen-containing compounds. 

In this chapter we review in some detail the results of our reaction dynamics studies employing various types of lasers to probe the formation of reaction products in different internal quantum states—electronic, vibrational, and rotational, depending on the processes investigated and on the diagnostic techniques used. Two different laser probing methods are used in this work they are resonance absorption and fluorescence methods using a cw CO laser and a tunable dye laser, respectively. 

The most widely used vibrational spectroscopic technique is time-resolved resonance Raman spectroscopy (TR ) [65]. This has been used successfully to obtain structural information about organic excited states in SCCO2. McGar-vey and co-workers probed the excited triplet state of anthracene in SCCO2 [66]. However, TR experiments involve data collection over many laser pulses, with all of the problems associated with secondary photolysis. These problems have prevented TR being used effectively to follow chemical reactions apart from highly photoreversible processes. To our knowledge, TR has not yet been used to follow chemical reactions in SCFs. Recently, however. 

The gas-phase photochemistry of pentacarbonyliron has received considerable attention on the femtosecond timescale. When irradiated in the gas phase with 260 nm radiation for 120 fs, the parent ion [Fe(CO)5] " is observed along with dissociation products [Fe(CO)s, t] (x= 1-5), whereas only Fe was observed using a 10 ns pulse. Similar results were obtained using a pump-probe technique at 400 and 800 nm with a 100 ns pulse. That study concluded that the ions [Fe(CO)5 .] occurred with concerted ligand loss, but that the loss of the last GO and formation of neutral Fe occurred in a stepwise fashion. These studies showed that [Fe(CO)5] was so short lived that it could not be observed when the timescale of the laser pulse was in the nanosecond regime. 

In laser measurements on hydrogen halides, the system under investigation is itself all, or part, of the active laser medium. Similar experiments have not yet been made on other molecules. However, in related experiments on CO, in the author s laboratory [242,432] and elsewhere [433], a CO cw laser has been used to probe the vibrational distributions in a reaction system outside the optical cavity that may act as an amplifier or absorber of lines from the laser. Time-resolved observations can be made for as long as one chooses after the reaction is initiated. If tunable infrared lasers become readily available this technique is likely to be applied more widely. 

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